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A controlled trial of Dulcodos, Dulcolax and Senokot DX

It is now accepted that adequate preparation for most barium enema examinations is essential, particularly if the double contrast technique is to be used (Fisher 1923; 1925; Case, 1937; Welin, 1958). Several studies have shown that preparation with laxatives may be as good as, or better than, colon washout (Sowerbutts, 1960; Prat, Peynon and Prie, 1965; Mitchell, 1967), and may cause the patient far less discomfort. Controlled trials have demonstrated the superiority of a standardised senna preparation (Senokot) over cascara (Duncan, 1957), and of bisacodyl (Dulcolax) over glycerine suppositories (Church, 1959) and over castor oil (Keogh and Fraser, 1958; Popell and Bangappa, 1959; Ritan, 1962). Recently laxative preparations including the faecal softener and detergent dioctyl sodium sulphosuccinate (Wilson and Dickinson, 1955; Hyland and Foran, 1968) have been introduced and it seemed of value to compare in a double blind trial three of the most widely used laxatives, Senokot DX (sennosides A and B 14 mg), Dulcolax (bisacodyl 5 mg) and a preparation consisting of bisacodyl 5 mg, and dioctyl sodium sulphosuccinate 100 mg (Dulcodos).



Four hundred and fifty sequential out-patients attending the Churchill Hospital for barium enema or intravenous pyelogram (IVP) were allocated on a pre-arranged random sequence to one of the three preparations and the trial was conducted on a double blind basis. The patients were told to take two laxative tablets on the two evenings preceding X-ray examination. On the day of the examination and before any cleansing enema was given, a plain abdominal radiograph 15×12 in. was taken.

The patient’s physical state, mobility, and reliability were assessed and the patient was questioned by an observer, who did not know which laxative had been taken, about the effectiveness of the laxative and any possible side effects. If the patient was undergoing a barium enema, a colon washout with three pints of water containing 10 mg Dihydroxyphenylisatin(P.C.L. 243, Damancy) was then performed and assessment was made by the nurse of the quantity of faeces removed by the washout. At a later stage the preliminary abdominal radiographs for both barium enemas and IVPs were examined by two radiologists (R.C.S. and F.W.W.), who did not know which preparation had been used, for the presence of gas and faeces in the colon, graded as none, slight, moderate or severe. The films of the barium enema examinations were reviewed at the same time and the presence of any faeces or pathology was noted.


It was decided to exclude 142 patients either because they did not attend or the tablets were not taken or because of clerical errors. The remaining 308 patients were almost equally divided between the three groups (see Table 1).

TABLE I Numbers of patients classified by sex and examination

Treatment Type of X-ray Total
IVP Barium enema  
Senokot DXDulcolax








Totals 181 127 308

In Table II, the results of our assessment of the plain films are shown; there was no significant difference between the three preparations either for gas or for faeces. It will be noted that about 40 per cent of patients have a bowel clear on the preliminary film.

TABLE II Assessment of faeces and gas on plain film

Treatment Faeces Gas
Total Clear % Clear %
Senokot DXDulcolax












A modification of Table II is shown on Table III, where we have classified the results of plain film assessment in terms of “satisfactory”, “unsatisfactory” or “gross faecal residue”. The assessment was satisfactory if the bowel was quite clear or contained only a minimal quantity of faeces insufficient in our view to prevent a satisfactory enema being performed. It was classed as unsatisfactory if the nurse who performed a colon washout recorded considerable faecal material, but the subsequent barium enema examination showed no radiological evidence of faecal contamination. “Gross faecal residue” was recorded if the colon was loaded with a substantial quantity of faeces, and even after a colon washout there was still considerable faecal residue so that a satisfactory barium enema examination was impossible. It will be seen that as in Table II, results with Senokot DX and Dulcodos were superior to those with Dulcolax, but the differences were not statistically significant.

TABLE III Detailed plain film faecal assessment

Treatment Satisfactory Unsatisfactory Gross faecal residue
Senokot DXDulcolax








Side-effects of the laxatives are shown in Table IV. 70 per cent of the patients were questioned about side-effects, and we have divided these into severe, moderate and minor. We have termed vomiting, griping pains or a trembling with cold sweats experienced by two patients as severe. Pain, nausea and dizziness we have classified as moderate side-effects. Diarrhoea or frequency of loose motions we have termed a “minor” side-effect, though this might be expected if a laxative is taken. More patients taking Senokot DX had severe side-effects than those taking Dulcolax or Dulcodos. Slightly more Dulcodos patients had more moderate side-effects than those taking Senokot DX. About a third of the patients complained of side-effects; none severe enough to prevent the patient working. Dulcolax had fewer side effects than Dulcodos or Senokot DX, but the difference is not statistically significant. It is interesting that in all groups twice as many women as men had side-effects.

TABLE IV Side-effects

  Senokot DX Dulcolax Dulcodos








TotalNone 3044 2148 3041
Overall total 74 69 71


Although this study has not shown a statistically significant difference in the efficiency of bowel preparation between the three laxatives under trial, it has suggested that Dulcolax is slightly inferior to the other two; on the other hand, there were fewer side effects with this drug. It should be noted that Senokot DX is much cheaper than the other preparations; however, tablets of Senokot tend to fragment if sent by post unless they are well packed.

One finding we consider interesting and important is that 40 per cent of the patients were clear of faeces on radiographs taken after laxative preparation; on the other hand, approximately 40 per cent were too severely contaminated for a satisfactory barium enema to be performed without a preliminary colon washout. It would seem that preparation with a laxative on its own is inadequate in such patients. However, in 40 per cent nursing time could be saved and the discomfort of a colon washout eliminated where the plain abdominal radiograph shows the colon clear of faeces. In such patients a barium enema may be performed straight away, whilst if moderate faecal contamination is present a colon washout should be undertaken, and if the colon is loaded with faeces the patient may be given further drug and enema preparation, for a colon washout will not clear the colon. It may, however, be wise to examine the distal colon at the first attendance to exclude a low neoplastic or other stricture causing gross faecal obstruction.

A further advantage of the preliminary abdominal radiograph is that in a few cases unexpected pathology may be found. In this series two groups of gall stones, a pelvic tumour and some unexpected renal calculi were discovered in this way. It might be argued that it is difficult to assess the quantity of faeces on the plain film accurately; this has not been our experience. In 84 per cent of the barium enema cases there was agreement between the patients’ own assessment, the opinion of the nurse about the quantity of the faeces removed by the wash-out, and the assessment of the preliminary abdominal radiographs. In the remaining 16 per cent the findings at barium enema closely followed the assessment of the plain radiograph even though the patient and the nurse were under the impression that the laxative had been effective.


1. No significant difference is found between Dulcolax, Senokot DX and Dulcodos in their effectiveness for bowel preparation for radiological examination; the latter two drugs appear to be slightly superior, but they suffer from the disadvantage of producing slightly more side-effects than Dulcolax.

2. It is suggested that a preliminary abdominal radiograph before a barium enema examination is of considerable value, for at least 40 per cent of patients have a sufficiently clear bowel after laxative preparation as not to require a colon washout. On the other hand, about 40 per cent are too contaminated for a satisfactory barium enema examination unless a colon washout is performed, and a small minority can be distinguished on the preliminary radiograph, who cannot be adequately prepared even with the aid of a colon washout.

Br. J. Radiol, 1970, 43, 245-247

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